1. Field of the Invention
The invention relates to an antenna system, and, more particularly, the present invention relates to an antenna system having at least two antennae and at least two receivers with self-testing circuitry.
2. Description of the Related Technology
An antenna system is known from DE 196 18 333 A1. This prior antenna system is a component with a mobile broadcast-receiving system and has at least one antenna. The signals received by the antenna are delivered to a receiver made as a superheterodyne receiver. The superheterodyne receiver has a mixer to which one bandpass filter at a time on the input side and the output side is connected. Moreover an oscillator is assigned to the mixer. The bandpass filter upstream of the mixer is used for mirror frequency suppression. The mixer mixes the signal which is at the input with the oscillator signal. The resulting intermediate frequency signal is filtered in the bandpass filter downstream of the mixer and then delivered to a signal processing unit for further processing.
To check operation of this antenna system, there is a switch that can be switched for control operation in which broadcast signals are received and evaluated, and to a test mode in which a self-test is carried out.
To carry out the self-test there is a separate transmitting antenna and a circuit arrangement connected to the transmitting antenna.
The circuit arrangement has a frequency converter which produces a high frequency output signal with which the transmitting antenna is energized.
The frequency converter is connected to the oscillator of the superheterodyne receiver. Moreover the frequency converter is connected to an intermediate frequency oscillator which is likewise a component of the circuit arrangement. Alternatively to the intermediate frequency oscillator there can be an intermediate frequency limiter which is connected to the output of the superheterodyne receiver.
The frequency of the high frequency output signal which is generated in the frequency converter is dictated by the intermediate frequency oscillator and the oscillator of the superheterodyne receiver and thus is tuned to the frequency of the superheterodyne receiver.
The high frequency output signal is capacitively coupled to the antenna of the antenna system via the transmitting antenna.
The signals at the output of the superheterodyne receiver are detected by a measurement device for carrying out the self-test.
The disadvantage in this antenna system is that an additional circuit arrangement with a separate transmitting antenna is necessary for carrying out the self-test. This results in undesirably high cost for carrying out the self-test.